RU2495457C2 - Monodirected neutron radiation detector - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: monodirected neutron radiation detector consists of a housing, a collector in form of a metal plate and a dielectric layer of a hydrogen-containing material, wherein the dielectric layer of hydrogen-containing material is enclosed in a current-conducting shell; the collector in form of a metal plate is enclosed in an insulating shell; between said shells there is an electrostatic screen; a connection line from the current-conducting shell enclosing the dielectric layer of hydrogen-containing material is connected to an inverting channel of a differential amplifier, and a connection line from the collector is connected to the non-inverting channel of the same amplifier.

EFFECT: eliminating effects associated with accumulation of negative charge in a dielectric and possible electric breakdowns, high sensitivity of the detector to neutron radiation.

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Description

The invention relates to the field of registration of ionizing radiation and can be used to determine the flux density of fast neutrons during the operation of nuclear physics facilities.

Known devices that allow the registration of neutron radiation using direct charge detectors, which implements radiation capture of neutrons or the fission reaction, followed by registration of currents in the form of electrons, protons, alpha particles or fission fragments [1].

The disadvantage of these direct charge detectors is their low temporal resolution, due to the relatively long half-life (more than 0.1 s) of the radioactive isotopes formed in the emitter.

Another type of direct charge detectors is known, in which instead of radiation capture of neutrons or fission reaction the effect of formation of Compton electrons in the emitter with their subsequent collection on the collector and with an acceptable time resolution is used [2, 3].

The disadvantage of this type of detectors is that although they are used to detect gamma rays or charged particles, they are not sensitive to electrically neutral particles such as neutrons, at least in the energy range from 100 keV to 20 MeV.

As a prototype for the largest number of matching features adopted detector of unidirectional neutron radiation [4].

The detector consists of a housing and a collector made in the form of a metal plate separated from the housing by a dielectric layer located on the irradiation side and made of a hydrogen-containing material, such as polyethylene. In a hydrogen-containing dielectric when irradiated with neutrons as a result of elastic and inelastic interactions with hydrogen atoms, high-energy recoil protons arise. The resulting protons move mainly in the direction of motion of the affected neutrons. A collector having a thickness equal to the range of the highest-energy recoil proton ensures complete absorption of the recoil protons coming to it and generates a positive electrical signal proportional to the acting neutron irradiation flux density.

The disadvantage of this prototype detector, firstly, is the relatively low sensitivity and the possibility of instability of the parameters of this detector due to the fact that in the dielectric layer made of polyethylene, from which the irradiating neutron flux knocks recoil protons, a negative charge accumulates as the radiation is irradiated exit from this polyethylene to positively charged particles - protons. In the volume of this dielectric, uncontrolled electrical breakdowns can also occur, which, coupled with an unstable level of accumulating electric charge, can lead to uncontrolled errors in determining the neutron flux density.

The second disadvantage of the prototype detector is the fact that a useful signal is detected only from one electrode - a collector, on which a positive charge of recoil protons is accumulated, and a negative charge formed in a dielectric layer from a hydrogen-containing material as a result of high-energy neutrons being knocked out of this layer recoil protons, not used at all.

The technical result to which the invention is directed is to eliminate the effects associated with the accumulation of a negative charge in the dielectric and the possible occurrence of electrical breakdowns, as well as increasing the sensitivity of the detector to neutron radiation.

The technical result is achieved as follows. A dielectric layer (made of hydrogen-containing material) is placed in the detector housing on the irradiation side, with a thickness equal to the range of the high-energy proton itself, and this layer is enclosed in a conductive shell, for example, of aluminized polyethylene, with an electrical output to the recording device. A collector, for example of aluminum, also with an electrical output to a recording device, is made equal in thickness to the range of the highest-energy proton, which ensures complete collection of all incoming protons in the collector. The collector is isolated from the detector body by a dielectric film. An electrostatic screen is placed inside the detector housing, which electrically decouples the dielectric layer of the hydrogen-containing material enclosed in the conductive sheath from the collector. The signal leads are connected to communication lines leading to a differential amplifier: from a conductive sheath covering a dielectric layer of a hydrogen-containing material, to an inverting input, and from a collector to a non-inverting input [5].

In a static mode of operation of a neutron radiation source, communication lines can be loaded with high-impedance resistances, up to the impedances equal in nominal value to the input resistances of the corresponding inputs of the differential amplifier. However, if the neutron emitter operates in a pulsed mode, the load resistances are selected equal to the wave impedance of the communication lines.

Figure 1 presents a General diagram of a detector of unidirectional neutron radiation, where:

1 - detector housing,

2 - a dielectric layer of a hydrogen-containing material,

3 - conductive sheath,

4 - electrostatic screen,

5 - insulating shell

6 - collector,

7 - communication line of the collector 6 with an input impedance 8 and a non-inverting input 11 of the differential amplifier 12,

8 - input resistance of the non-inverting input 11 of the differential amplifier 12,

9 - input resistance of the inverting input 13 of the differential amplifier 12,

10 - communication line of the shell 3 with an input impedance 9 and an inverting input 13 of a differential amplifier 12,

11 - non-inverting input of the differential amplifier 12,

12 - differential amplifier

13 - inverting input of the differential amplifier 12.

The detector operates as follows: to register the neutron flux, the detector is placed in a given place of the radiation field. As a result of directing neutron radiation in the hydrogen-containing material 2, recoil protons arise, which penetrate through the conductive shell 3, then through the electrostatic screen 4, the insulating shell 5 and are absorbed by the collector 6. As a result, a negative space charge is formed in the dielectric layer 2, and on the collector 6 - positive.

In the considered embodiment, polyethylene is used as the dielectric layer 2. This polyethylene layer 2 is enclosed in a conductive sheath 3. Due to electrostatic induction, a negative charge will arise in the sheath 3, which is exactly equal to the total volume charge formed when neutrons are irradiated in the hydrogen-containing layer 2. As a result, an external EMF with a negative pole on the sheath is created 3 and positive - on the collector 6. A closed loop of the working current passes through the elements: from the plus pole on the collector 6 through the communication line 7 through the input resistance 8, then through the input resistance 9 and via communication line 10 to minus EMF, i.e. to the shell 3. Thus, the operating current creates at the input resistances 8 and 9 two of the same amplitude (if these resistances are the same), but of a multipolar signal. A signal of positive polarity from the input resistance 8 through the communication line 7 is fed to the input of the non-inverting channel 11 of the differential amplifier 12, and a signal of negative polarity from the input resistance 9 through the communication line 10 is fed to the input of the inverting channel 13 of the same differential amplifier 12. These two bipolar signals differential amplifier 12 modulo add up.

In this scheme, the conductive shell 3, due to its shielding properties, completely eliminates interference from breakdowns as well as from the inhibitory effect of the accumulated electric charge on the proton exit from the hydrogen-containing dielectric 2 from the electric field, and, therefore, the number of errors affecting the results is reduced measuring the useful signal.

The proposed detector allows you to receive and register twice the amplitude of the useful signal with less electrical noise in the signal registration system compared to the prototype detector.

Literature

1. Mitelman M.G., Rosenblum N.D. Charge detectors of ionizing radiation. M., Energy Publishing House, 1982, 78 pp.

2. Ioilev G.F., Safonov V.A. The detector with a dielectric diffuser. Instruments and experimental equipment, 1969, No. 5, p. 210.

3. Gross B. J. Applied Phjsics, 1965, v. 36, N5.

4. Yakovlev M.V., Tereshkin I.S. Monodirectional neutron radiation detector. Auth. Certificate No. 713293 dated January 10, 2005, class G01T 3/00.

5. Jones M.H. Electronics - a practical course. Moscow: Postmarket, 1999 .-- 528 p.

Claims (1)

A monodirectional neutron radiation detector, consisting of a body, a collector made in the form of a metal plate, and a dielectric layer of hydrogen-containing material, characterized in that the dielectric layer of hydrogen-containing material is enclosed in a conductive sheath, a collector in the form of a metal plate is enclosed in an insulating sheath, between these sheaths housed an electrostatic screen, a communication line from a conductive sheath covering a dielectric layer of a hydrogen-containing material, connected to the inverting channel of the differential amplifier, and the communication line from the collector is connected to a non-inverting channel of the same amplifier.